Effects of dietary vitamin C on growth, gonad development and antioxidant ability of on‐growing gibel carp ( Carassius auratus gibelio var. CAS III )

An 88‐day experiment was conducted in a flowing system to evaluate the effects of dietary vitamin C on growth, body composition, antioxidant and gonad development of on‐growing gibel carp. Triplicate tanks of gibel carp (77.2 ± 0.1 g) were randomly fed with one of seven experimental diets containing l ‐ascorbic acid of 0, 101.1, 188.5, 313.1, 444.1, 582.1 and 747.0 mg/kg, respectively. The results showed that specific growth rate ( SGR ) and feed efficiency ( FE ) of fish were not affected by dietary l ‐ascorbic acid. Dietary l ‐ascorbic acid of 444.1 mg/kg diet led to low levels ( p <  .05) of gonadosomatic index ( GSI ) and hypothalamic gonadotropin‐releasing hormone (Gn RH ) in on‐growing fish, as well as the early ovarian stages (Developing stages) compared with fish (Maturing stages) from the other groups. Dietary l ‐ascorbic acid supplementation increased ( p <  .05) the dorsal muscle collagen content, but did not affect the protein or lipid content of dorsal muscle in gibel carp. Plasma total antioxidant capacity (T‐ AOC ) and superoxide dismutase ( SOD ) activity increased ( p <  .05) and then remained unchanged with the increase in dietary l ‐ascorbic acid levels. Dietary l ‐ascorbic acid of 101.1 mg/kg diet improved ( p <  .05) plasma lysozyme activity of the fish. Broken‐line regression indicated that dietary l ‐ascorbic acid requirement of 77 g gibel carp was 223.3 or 225.0 mg/kg diet based on plasma T‐ AOC or SOD activity, which was a little higher than that based on plasma l ‐ascorbic acid concentration (193.2 mg/kg).